Lateral field emitter device and method of manufacturing same

ABSTRACT

Lateral luminescent field emitter devices for use in flat panel displays and a method of manufacturing are described. The device comprises a flat substrate, an anode disposed on the substrate, and a cathode disposed on the substrate, the cathode providing an electron emission surface capable of emitting electrons laterally across a gap to a major portion of an adjacent surface of the anode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to field emitters, and more particularly tolateral luminescent field emitter devices in flat panel displays.

2. Description of Related Art

There are several means by which electrons may be emitted from amaterial by increasing the energy of electrons at the material surfaceso that the energy exceeds a certain energy potential barrier. Forexample, thermionic emission uses heat, photoemission uses radiationsuch as light, and secondary emission uses charged particles such aselectrons or ions to increase the electron energy level at the emissionsurface. Electron emission by such means has been used for cathode raytubes in television sets for example.

Field emission devices ("FED's") liberate electrons by lowering thepotential barrier at a conductive emission surface rather than byraising the electron energy. In accordance with the probabilities ofquantum mechanics, although the energy of electrons in a conductivematerial does not exceed the potential barrier at the conductor surfacenevertheless a certain portion of those electrons will tunnel throughthat potential barrier to be emitted at the surface. An electrical fieldmay be employed to narrow the potential barrier so that an increasingportion of the electrons are emitted, thereby increasing field emissioncurrent. Such FED's have been used for purposes such as electronmicroscopes and flat panel displays. They have been extensively studiedand are well known in the art. See, for example, R. J. Noer, "ElectronField Emission from Broad Area Electrodes", Applied Physics A 28, pp.1-24 (1982).

FED's have a number of limitations which restrict their usefulness. Onelimitation concerns the energy level imparted to the electrons afterthey are emitted. Another limitation concerns the uniformity of emissioncurrent. The mechanisms and tradeoffs of these and other limitationswill be further explained in the following discussion.

One limitation concerns ionization due to electron energy. The energywhich the electric field imparts to electrons after emission may reach alevel that causes gases surrounding the electron emission surface toionize. Such ionized gases may in turn damage the emission surface andimpair further emission. See, for example, U.S. Pat. No. 3,970,887, byD. Smith, et al., entitled "Micro-Structure Field Emission ElectronSource" (discussing shortened life due to ionization). Therefore, toreduce the required electrical field and thereby reduce the amount ofionization, typical FED's use low "work function" materials for theemission surface, that is, special materials that emit electrons atrelatively low energy levels. R. Gomer, FIELD EMISSION AND FIELDIONIZATION, Harvard Univ. Press, pp. 3-4 (1961); see also, U.S. Pat. No.4,663,559, by A. Christensen, entitled "Field Emission Device".

The electrical field required for emission may also be reduced byshaping the emission surface so that the field is concentrated into asmall region. See, for example, U.S. Pat. No. 3,998,678, by S. Fukase,et al., entitled "Method of Manufacturing Thin-Film Field EmissionElectron Source" (conical tips); U.S. Pat. No. 4,663,559, by A.Christensen, entitled "Field Emission Device" ("whiskers" in prior artand particles in the Christensen device); and U.S. Pat. No. 5,066,883,by S. Yoshioka, et al., entitled "Electron-Emitting Device withElectron-Emitting Region Insulated from Electrodes" (thin film withcracks); and U.S. Pat. No. 5,089,742, by D. Kirkpatrick, et al.,entitled "Electron Beam Source Formed with Biologically Derived TubuleMaterials" (micro-protrusions); V. Makhov, "Field Emission CathodeTechnology and its Application", Technology Digest of IVMC 91, Nagahama1991 (edge of film). This results in emission at an applied voltagelower than the voltage required for a reference configuration with flatshapes, thereby defining a "field enhancement factor". See H. Busta, etal., "Field Emission from Tungsten-Clad Silicon Pyramids", IEEETransactions on Electron Devices, Vol. 36, No. 11, pg. 2679 (November1989).

One drawback of concentrating the field in a small region is that thecurrent emission is also limited to a small region resulting in a lowcurrent, high density electron beam. See U.S. Pat. No. 3,755,704, by C.Spindt, et al., entitled "Field Emission Cathode Structures and DevicesUtilizing Such Structures" (discussing techniques to provide multiplepoints for parallel currents in order to increase total currentavailable). And the typical sharp pointed emitters also suffer fromuniformity limitations. See H. Kosmahl, "A Wide-Bandwidth High-GainSmall-Size Distributed Amplifier with Field-Emission Triodes (FETRODE's)for the 10 to 300 GHz Frequency Range", IEEE Transactions on ElectronDevices, Vol. 36, No. 11, pg. 2728 (November 1989) (explaining thatsharp pointed structures do not provide uniform emission currents fromone device to the next, and discussing how the variation relates totopography). Thus, such beams are not ideally suited for producingluminesence over a large area.

Besides using low work function material and field enhancing shapes toreduce the required electrical field for electron emission, FED'stypically employ a small separation between the emission electrode andthe accelerator electrode (i.e., "field electrode", or "gate") whichproduces the liberating electrical field. In this manner the electricalfield is increased without increasing the voltage driving the field sothat less energy is imparted to the electrons after emission. One meansfor providing such a small separation involves etching a laminatestructure with a first electrode on a flat substrate, a thin dielectriclayer over the first electrode, and a second electrode layer over thedielectric so that the bottom electrode is exposed in close proximity tothe top electrode. See, for example, U.S. Pat. No. 4,307,507, by H.Gray, et al., entitled "Method of Manufacturing a Field-Emission CathodeStructure"; U.S. Pat. No. 4,943,343, by Z. Bardai, et al., entitled"Self- Aligned Gate Process for Fabricating Field Emitter Arrays"; andU.S. Pat. No. 4,964,946, by H. Gray, et al., entitled "Process forFabricating Self-Aligned Field Emitter Arrays"; U.S. Pat. No. 5,066,883,by S. Yoshioka, et al., entitled "Electron-Emitting Device withElectron-Emitting Region Insulated from Electrodes". Another means forproviding a small separation between electrodes involves etching abuffer layer between electrodes on the same substrate to provide lateralelectron emission. See, for example, Makhov, "Field Emission CathodeTechnology and its Application", Technical Digest of IVMC 91, Nagahama1991; S. Bandy, "Thin Film Emitter Development", Technical Digest ofIVMC 91, Nagahama 1991.

There are tradeoffs involved in lowering the voltage required to produceelectron emission. It is desirable to reduce the voltage not only inorder to reduce gas ionization, but also because it increases frequencyresponse by reducing the time required to bring the field electrode upto the required emission voltage. As described above, reducing theseparation between the emission electrode and the field electrode helpsto reduce the required voltage; however, a decreasing separation has theundesireable side effect of increasing sensitivity of the FED emissioncurrent to small variations in electrode separation. FED current densitymay change by as much as 10% for a 1% change in electrode separation.Furthermore, although it is desirable to lower the energy level impartedto emitted electrons in order to preserve the emission surface, it isalso desirable to impart a relatively high energy level to the electronsso that they may deliver more energy to generate more light in a displayfor example. Higher energy is especially needed where the total emissioncurrent is limited by current density when field enhancing shapes areemployed. See U.S. Pat. No. 3,665,241, by C. A. Spindt, et al., entitled"Field Ionizer and Field Emission Cathode Structures and Methods ofProduction" (discussing low current because of the minute size of asharp pointed emitting area, and low energy because of the smallseparation between emitter and accelerator electrodes). Thus to raisethe allowable operating voltage and limit ionization damage to emissionsurfaces a high vacuum is typically employed. See, for example, U.S.Pat. No. 4,663,559, by A. Christensen, entitled "Field Emission Device"(discussing typical vacuum operation).

To accommodate these tradeoffs FED's have typically been triodearrangements wherein a high voltage anode is employed above a field(i.e., "accelerator") electrode. In these devices a low voltage fieldelectrode is placed on the same substrate in a layer above the emissionsurface electrode. A small separation between the emitter ("cathode")and field electrodes may thus be precisely controlled so that emissionoccurs uniformly and at a low voltage. A higher voltage electrode("anode") is then provided on another substrate aligned above the first.See, for example, U.S. Pat. No. 5,066,883, by S. Yoshioka, et al.,entitled "Electron-Emitting Device with Electron-Emitting RegionInsulated from Electrodes" (for example FIG. 3B indicating electronemission 7 toward a third electrode not shown); U.S. Pat. No. 4,780,684,by H. Kosmahl, entitled "Microwave Integrated Distributed Amplifier withField Emission Triodes" (conical or pyramid shaped emitters in triodestructure); and H. Kosmahl, "A Wide-Bandwidth High-Gain Small-SizeDistributed Amplifier with Field-Emission Triodes (FETRODE's) for the 10to 300 GHz Frequency Range", IEEE Transactions on Electron Devices, Vol.36, No. 11, pg. 2728 (November 1989).

Although emission current uniformity is increased by providing a lowvoltage field electrode precisely located nearby the cathode,nevertheless, in these triode FED's spacing between the anode andcathode is still very important. Variations in anode-cathode spacing maycause image distortion and non-uniform brightness in flat paneldisplays. Spacers used to secure the anode-cathode separation may permitleakage current which increases power consumption, distorts theelectrical field, and contributes to electrode breakdown. And since avacuum of less than 10⁻⁶ torr is generally applied between the anode andcathode substrates the spacers must be strong and numerous to withstandthe forces on the substrates. Thus precise spacing is problematic forthe triode FED's used in flat panel displays where the anode and cathodeare on two different substrates. See, for example, U.S. Pat. No.4,923,421, by I. Brodie, et al., entitled "Method for ProvidingPolyimide Spacers in a Field Emission Panel Display".

Thus the above structures and atmospheres are useful for flat paneldisplay applications, but they may be further improved. The fieldenhancing structures such as conical tips, film edges, whiskers, etc.provide only a low current, high density electron beam. Such beams arenot ideally suited for producing luminesence over a large area. Alsothese structures suffer from uniformity limitations. Triodes are notideally suited to flat panel displays because they require precisealignment in two planes and the spacers are problematic. Furthermore,none of these structures provide a broad area emission surface to directelectrons laterally to a luminescent anode located, as is desirable fora flat panel display.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a means todirect electrons from a broad emission surface to a major portion of asurface of a laterally disposed anode.

Other objects include providing a lateral field emitter device and amethod for manufacturing such that the device has uniform fieldemission, has a large field enhancement factor, requires only arelatively small voltage for field emission to occur, and is suitablefor a multicolor array of lateral, luminescent field emitter diodes foruse in a full-color flat panel display using low voltage IC drivers.

A feature of the present invention is a lateral field emission diodewith a flat substrate made of an insulating material having a layer of aconductive material covering a portion of the substrate, an anodedisposed on the layer of conductive material, and a cathode disposed onan insulative layer over the conductive layer, the cathode providing anelectron emission surface and being so disposed as to provide a means todirect electrons from the emission surface laterally to the anode.

Another feature of the present invention is providing a lateral fieldemitter device including a flat substrate which is a transparentinsulator. The substrate has a conductive layer covering a portion ofthe substrate, an anode disposed on the conductive layer, and a cathodedisposed on an insulative film which is on the conductive layer. Atleast one side of the cathode extends upward from the substrate andfaces a corresponding side of the anode, which also extends upward fromthe substrate. These corresponding sides are disposed a uniform distanceapart so that the gap between the cathode and anode is uniform. When acertain electrical potential is applied between the anode and thecathode, the cathode emits electrons to the anode along the length ofthe gap. Upon emission the electrical field imparts a predeterminedenergy level to the emitted electrons. Also, gases in the gap have anionization potential above the energy level of the emitted electrons,thus the electrons emitted to the anode do not ionize the gases.Alternatively, a vacuum is provided so that the gases in the gap have acertain density. That density is less than a predetermined criticaldensity so that the emission surface is preserved despite a small amountof ionization.

Another feature of the present invention in accordance with oneembodiment is a method of manufacturing a lateral field emitter deviceincluding the steps of (a) providing a substantially flat substrate, (b)disposing a conductive layer on the substrate, (c) disposing an anodematerial on the conductive layer, (d) positioning an etch mask with anopening therethrough above the anode material such that the anodematerial beneath the opening is exposed whereas the anode materialbeneath the mask is covered, (e) etching the anode material beneath theopening wherein the etching undercuts the anode material beneath themask thereby forming an anode sidewall beneath the mask, exposing theconductive layer beneath the opening and exposing the conductive layerbeneath the mask adjacent the anode sidewall, (f) depositing aninsulative film on the conductive layer beneath the opening withoutdepositing the insulative film on the anode sidewall thereby forming aninsulative film sidewall defined by the opening, (g) depositing acathode material on the insulative film beneath the opening withoutdepositing the cathode material on the anode sidewall thereby forming acathode sidewall defined by the opening and a substantially uniform gapbetween the anode sidewall and the cathode sidewall wherein the cathodematerial has a bottom surface between a top and bottom surface of theanode material, and (h) removing the mask.

A further feature of the present invention in accordance with anotherembodiment is a method of manufacturing a lateral field emitter devicethat is similar to the above method, but which enables a smaller gapwhile requiring more steps. This method includes the steps of (a)providing a substantially flat substrate, (b) disposing a conductivelayer on the substrate, (c) disposing an anode material on theconductive layer, (d) positioning an etch mask with an openingtherethrough above the anode material such that the anode materialbeneath the opening is exposed whereas the anode material beneath themask is covered, (e) etching the anode material beneath the openingthereby forming an anode sidewall defined by the opening and exposingthe conductive layer beneath the opening, (f) depositing an insulativefilm on the conductive layer beneath the opening and on the entire anodesidewall thereby forming an insulative film sidewall with a lowerportion adjacent the conductive layer and an upper portion adjacent theopening, (g) depositing a cathode material on the insulative film on theconductive layer beneath the opening and on the lower portion of theinsulative film sidewall without depositing the cathode material on theupper portion of the insulative film sidewall thereby forming a cathodesidewall adjacent the lower portion of the insulative film sidewallwherein the cathode material has a bottom surface between a top andbottom surface of the anode material, (h) removing the upper portion ofthe insulative film sidewall, (i) removing the mask, and (j) removingthe lower portion of the insulative film sidewall thereby forming asubstantially uniform gap between the anode sidewall and the cathodesidewall.

In another feature of the present invention, either of the above methodsmay further include providing the anode and the cathode in fork shapesdisposed so that they interleave to form a rectangle. Additionally, theinterleaving shapes may be arranged so that at least 50% of the area ofthe resulting rectangular field emitter is capable of luminescing.

A still further feature of the present invention is a method ofmanufacturing an entire array of lateral field emitter devices. Thefield emitter devices in the array may be of varied luminescent colorsso that they may be used in a full-color, flat panel display. In orderto make the array, the step of depositing the anode material is alteredand repeated.

The present invention makes use of thin film technology principles whichhave been known and studied for many years and published in severalbooks. See, for example, Maissel and Glang, Handbook of Thin FilmTechnology, 1983 Reissue, McGraw-Hill Book Company, which isincorporated herein by reference.

An advantage of the present invention is that it provides an efficientmethod of manufacturing a small gap between the anode and the cathode ofa field emitter which does not require high resolution photoreduction.

Another advantage is that it provides a method of manufacturing a fieldemitter which does not require accurately aligning elements of thedevice in two planes.

A still further advantage is a relatively low temperature method ofmanufacturing which can be performed without melting a glass substrate(melting point approximately 500° C.).

A still further advantage is that it provides a low cost, high yieldmethod for manufacturing an array of field emitter devices for largearea (10 inch diagonal or greater) flat panel displays on a singlesubstrate using standard semiconductor technologies.

These and other objects, features, and advantages of the presentinvention will be further described and more readily apparent from areview of the detailed description and preferred embodiments whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the preferred embodiments can bestbe understood when read in conjunction with the accompanying drawings,wherein:

FIG. 1 shows a perspective view of a lateral field emitter device of thepresent invention having an anode and cathode disposed side by side.

FIG. 2 shows a perspective view of a lateral field emitter device of thepresent invention having an interleaving, forked-shaped anode andcathode.

FIGS. 3A-3G show cross-sectional views of successive first stages offabricating a field emitter device of the present invention.

FIGS. 4A-4D show cross-sectional views of successive second stages offabricating a field emitter device of the present invention inaccordance with a first embodiment.

FIGS. 5A-5F show cross-sectional views of successive second stages offabricating a field emitter device of the present invention inaccordance with a second embodiment.

FIGS. 6A-6C show enlarged top plan views of the field emitter device ofthe present invention with flat and serrated sidewalls defining the gapbetween the anode and the cathode.

FIGS. 7A-7C shown enlarged top plan views of a portion of the fieldemitter device of FIGS. 6A-6C illustrating calculated lines of equalpotential between the anode and the cathode.

FIG. 8 shows a cross-sectional view of the field emitter device of thepresent invention illustrating a stream of electrons and photons duringoperation.

FIG. 9 shows an elevated perspective view of an array of the fork-shapedfield emitter devices of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the accompanying drawings similar elements are designated by the samereference numeral throughout the several views. Elements depicted arenot necessarily shown to scale.

Referring to FIG. 1, there is shown a field emitter device 10. At thebase of device 10 is a flat substrate 12. A portion of substrate 12 iscovered by an electrically conductive layer 14. Disposed on conductivelayer 14 is anode 16. Disposed on another portion of conductive layer 14is electrically insulative layer 20, upon which is disposed cathode 22.Anode 16 has a flat side 24 which extends orthogonally upward from thetop surface of substrate 12. Likewise, cathode 22 has a flat side 26which extends orthogonally upward from the top surface of substrate 12.Side 24 of anode 16 is spaced from and parallel to corresponding side 26of cathode 22. As a result, gap 30 extends above conductive layer 14between anode side 24 and cathode side 26. As also seen, top surface 32of anode 16 extends above top surface 34 of cathode 22, and bottomsurface 36 of anode 16 extends below bottom surface 38 of cathode 22.

Referring to FIG. 2, there is shown another embodiment of field emitterdevice 10 with an interleaving, fork-shaped anode and cathodeconfiguration. In this embodiment, the length of anode legs 40, 42 and44 exceeds the height of anode 16; likewise, the length of cathode legs46 and 48 exceeds the height of cathode 22. Anode sides 24a, 24b, 24c,24d, 24e, 24f, and 24g are spaced from and parallel to correspondingcathode sides 26a, 26b, 26c, 26d, 26e, 26f, and 26g. The correspondinganode sides 24a-24g and cathode sides 26a-26g define gap 30 which isuniform and extends the entire length of anode sides 24a-24g.

Because of its lateral structure and the long uniform gap between theanode and the cathode, field emitter device 10 is well suited to providepixel shapes for flat panel displays. The anode and cathode of FIG. 2form a rectangle having 150 micrometer long sides 49a and 49b. Such afield emitter device has more than 50% luminescent surface area. The gap30 may include only gases with ionization potentials of more than 10volts--for example, air at normal atmospheric pressure. Accordingly,when an electrical potential of 10 volts is applied between the anodeand cathode with such a gap the cathode emits electrons which will beimparted an energy level of 10 eV or less. Because the energy levelimparted to the emitted electrons is below the ionization potential ofthe air there is no ionization of gases in the gap. Alternatively, if itis desired to operate the FED at a higher voltage to increaseluminescence of the anode, the gap 30 may be evacuated to a pressure of10⁻⁶ torr or less so that the gases in the gap have a density less thana predetermined critical density. The emission surface will then bepreserved despite a small amount of ionization.

Further details of the structure of field emitter device 10 will bedescribed and depicted in the following methods for producing thelateral field emitter device of the present invention.

Referring to FIGS. 3A-3G, there are shown successive cross-sectionalviews depicting the first stages for partially fabricating field emitterdevice 10. These first stages are common to a first and secondembodiment for fabricating device 10, with the final stages shown inFIGS. 4A-4D and FIGS. 5A-5F, respectively.

With reference to FIG. 3A, substrate 12 is provided with conductivelayer 14 thereon. Substrate 12 is preferably an insulator such as glassor silicon, or an appropriate metal, although other materials can beused provided they furnish a substantially flat, stable surface uponwhich a plurality of field effect devices can be fabricated. Acontinuous, 0.1 micrometer thick conductive layer 14 is disposed on theentire top surface of substrate 12 using thin or thick film depositiontechniques. In the event luminescence from the bottom of device 10 isdesired, substrate 12 and conductive layer 14 must each be transparent,in which case substrate 12 is preferably glass and conductive layer 14is preferably indium tin oxide deposited by sputtering or evaporation.If, on the other hand, luminescence from the top of device 10 is desiredthen conductive layer 14 is preferably a reflective material such asaluminum. If only a single anode and cathode are desired then substrate12 and conductive layer 14 may be the same conductive material.

With reference to FIG. 3B, a several micrometer thick continuous layerof photoresist 50 is overlayed on conductive layer 14. Thinnerphotoresist masks are acceptable provided the film is continuous.

With reference to FIG. 3C, photoresist 50 is patterned through standardlithographic techniques to form photoresist etch mask 52 containing apredetermined pattern of openings 54 thereby exposing portions 56 ofconductive layer 14 while covering portions 58 of conductive layer 14.

With reference to FIG. 3D, the exposed portions 56 (FIG. 3C) ofconductive layer 14 are etched and removed thereby exposing theunderlying portions 60 of substrate 12. Any suitable dry or wet chemicaletch can be used, as is conventional.

With reference to FIG. 3E, photoresist etch mask 52 (FIG. 3D) isremoved, such as by dissolving the mask in a solvent as is well known inthe art, thereby exposing unetched portions 58 of conductive layer 14.

With reference to FIG. 3F, anode material 62 is disposed on conductivelayer 14. For instance, anode material 62 may be deposited as a layer 2micrometers to 10 micrometers thick on the entire unetched portion 58 ofconductive layer 14 without being deposited on the exposed portions 60of substrate 12, for instance using thin or thick film techniques suchas sputtering anode material 62 through a patterned metal mask (notshown). Anode material 62 may be a low energy conductive phosphor whichemits light upon bombardment by electrons, preferably with energy ofapproximately 400 electron-volts or less. (Herein, emitting light due toelectron bombardment is referred to as "luminescing".) Suitable lowenergy phosphors include ZnO:Zn, ZnCd:Ag, and ZnS:Ag,Al.

With reference to FIG. 3G, using the photolithographic method describedin FIGS. 3B and 3C above, a second etch mask, shown as photoresist etchmask 64, is overlayed on anode material 62. Etch mask 64 is patternedwith openings 66 exposing portions 68 of anode material 62. For example,to obtain the fork-shaped anode of FIG. 2, mask 64 would be similarlypatterned.

It should be understood that the anode material and conductive layer arenot normally etched and patterned in the same step since the conductivelayer typically includes interconnecting portions outside the anodematerial. Furthermore, if a full-color flat panel display is desiredthen the steps in FIGS. 3F and 3G can be performed in sequence threetimes to selectively pattern three different anode materials. This mayinclude depositing a discontinuous layer of red, blue and green phosphoron different portions of the conductive layer.

As mentioned above, FIGS. 3A-3G provide the first stages for fabricatinga field emitter device in accordance with a first and second embodimentof the present invention. The second stages of the first embodiment areshown in FIGS. 4A-4D; the second stages of the second embodiment areshown in FIGS. 5A-5F. The field emitter devices produced in the firstand second embodiments have similar structures except the gap betweenthe anode and the cathode in the second embodiment may be relativelysmaller.

With reference to FIG. 4A, the exposed portions 68 (FIG. 3G) of anode 62are etched, preferably in wet chemicals, thereby exposing first portions70 of conductive layer 14 directly beneath mask openings 66. Inaddition, the etch is a side-etching process that undercuts sides 24 ofanode material 62 thereby forming anodes 16 beneath mask 64 and exposingsecond portions 74 of conductive layer 14 beneath mask 64. Thus, secondconductor portions 74 are adjacent to anode sides 24. Second conductorportions 74 are preferably 0.8 micrometer to 1.2 micrometer in lengthand define the lateral location of gap 30 between anode 16 and cathode22.

With reference now to FIG. 4B, an electrically insulative film 80 isdeposited on device 10, including the top surfaces of mask 64 and firstportions 70 of conductive layer 14. However, insulative film 80 is notdeposited on a substantial portion of anode sides 24 or second conductorportions 74, which remain "shielded" by mask 64. Preferably, essentiallyno portion of anode sides 24 or second conductor portions 74 arecontacted by insulative film 80 and gap 30 remains substantiallyuniform. In addition, insulative film 80 must not provide step coverageor "bridges" between upper insulative film 82 on mask 64 and lowerinsulative film 84 on first conductor portions 70. Thus, insulative filmportions 82 and 84 are spaced apart and separate from one another. As aresult, sides 86 of lower insulative film 80 are spaced from anode sides24 by gap 30. Preferably, insulative film 80 is approximately 1micrometer thick and is deposited by a thin film physical vapordeposition technique such as sputtering or evaporation through a metalmask (not shown). Preferred materials for insulative film 80 includesilicon dioxide (SiO₂) or silicon nitride (Si.sub. 3 N₄).

With reference now to FIG. 4C, a layer of cathode material 90 isdeposited on device 10, including the top surfaces of upper insulativefilm 82 and lower insulative film 84. As a result, cathodes 22 aredisposed on lower insulative film 84. Cathode material 90 may bedeposited by a thin film physical vapor deposition technique such assputtering or evaporation through a metal mask (not shown). Suitablecathode materials include molybdenum, tungsten, diamond or cermet. Theuse of diamond as a cathode material is disclosed in U.S. Pat. No.5,199,918 by N. Kumar, entitled "Method of Forming Field Emitter DeviceWith Diamond Emission Tips" and in U.S. Pat. No. 5,180,951 by L.Dworsky, et al., entitled "Electron Device Electron Source IncludingPolycrystalline Diamond"; cermet cathode materials are described in U.S.Pat. No. 4,663,559 by A. Christensen, entitled "Field Emission Device" Adiamond cathode material may be deposited, for instance, as disclosed inU.S. Pat. No. 5,098,737 to C. Collins, et al., entitled "AmorphicDiamond Material Produced By Laser Plasma Deposition", and in U.S. Pat.No. 4,987,007 to S. Wagal et al., entitled "Method And Apparatus ForProducing A Layer Of Material From A Laser Ion Source." Preferably, thethickness of cathodes 22 is no more than approximately 10% of thethickness of lower insulative film 84, and the combined thickness ofcathodes 22 and lower insulative film 84 is no more than 80% of thethickness of the anodes 16. Cathode material 90, like insulative film80, should not spread or provide step coverage so as to interfere withgap 30. That is, cathode material 90 is not deposited on a substantialportion of anode sides 24 or second conductor portions 74, which remain"shielded" by mask 64 and upper insulative layer 82. Preferably,essentially no portion of anode sides 24 or second conductor portions 74are contacted by cathode material 90, cathode sides 26 and insulatingfilm sides 86 are substantially aligned, and gap 30 remainssubstantially uniform. In addition, cathode material 90 should notspread or provide step coverage ("bridges") between the cathode materialon mask 64 and the cathode material on first conductor portions 70. Asis seen, upper and lower cathode material 92 and 94, respectively, arespaced and separate, and are deposited on upper and lower insulativefilm 82 and 84, respectively. In addition, sides 26 of cathodes 22 arespaced from anode sides 24 by gap 30. In this manner, a gap ofapproximately 1.0 micrometer is readily provided.

With reference now to FIG. 4D, mask 64 is stripped and removed, forinstance by dissolving mask 64 in a solvent. This "liftoff" of mask 64also removes upper insulative film 82 and upper cathode material 92thereon. The completed field emitter device 10 thus includes cathodes 22disposed on lower insulative layer 84 and laterally separated fromanodes 16 by gap 30 extending from exposed portions of conductive layer14 to top surface 34 of cathodes 22.

FIGS. 5A-5F show cross-sectional views of successive second stages offabricating a field emitter device in accordance with a secondembodiment of the present invention.

With reference now to FIG. 5A, the exposed portions 68 (FIG. 3G) ofanode material 62 are etched away to form sides 24 of anodes 16 directlybeneath openings 66. (Unlike the first embodiment, the etch need not andpreferably does not undercut the sides of the anode material beneath themask.) As a result, portions 70 of conductive layer 14 beneath maskopenings 66 are exposed whereas the portions of layer 14 beneath mask 64remain covered by anode material 62. Anisotropic dry etching ispreferred to assure anode sides 24 correspond directly to mask openings66.

With reference now to FIG. 5B, a continuous layer of insulative film 80is deposited over the entire device. (Unlike the first embodiment,insulative film 80 completely covers anode sides 24 and extends throughopenings 66.) As is seen, in the second embodiment insulative film 80not only includes upper and lower insulative film 82 and 84,respectively, but also insulative film sidewalls 100 extending fromconductive layer 14 to the top of mask 64. Thus, in sharp contrast tothe first embodiment, insulative film 80 not only contacts anode sides24 but covers all of anode sides 24. Therefore, in FIG. 5B insulativefilm 80 is preferably deposited by plasma enhanced chemical vapordeposition (as opposed to sputtering or evaporation as in FIG. 4B) toassure proper step coverage.

With reference now to FIG. 5C, cathode material 90 is deposited ondevice 10. (Unlike the first embodiment, cathode material 90 does notcorrespond to openings 66 due to insulative film sidewalls 100 therein.)As may be seen, in the second embodiment cathode material 90 does notcover all of insulating film 80. That is, upper portion 102 ofinsulating film sidewalls 100 between upper cathode material 92 andlower cathode material 94 remains exposed. However, lower portion 104 ofinsulating film sidewalls 100 is sandwiched between anode sides 24 andcathode sides 26. Thus, in the second embodiment, lower insulating filmsidewall portion 104 shall define gap 30.

With reference now to FIG. 5D, upper insulating film sidewall portion102 is removed, such as by wet chemical etching. Upper cathode material92, however, covers and protects upper insulating film 82. Likewise,lower cathode material 94 covers and protects lower insulating film 84.Furthermore, little or none of lower insulating film sidewall portion104 is removed in this step.

With reference now to FIG. 5E, mask 64 is stripped and removed, forinstance by dissolving the mask in a solvent. This liftoff step alsoremoves layers 82 and 92 on mask 64. Such liftoff would be difficult orimpossible if upper insulating film sidewall 102 were to remain ondevice 10 since sidewall 102 would shield mask 64 from the etch as wellas clamp mask 64 to device 10.

With reference now to FIG. 5F, lower insulating film sidewall portion104 is stripped and removed, such as by wet chemical etching, therebycreating gap 30 between anode sides 24 and cathode sides 26. It isunderstood that similar wet chemical etchants may be used in FIGS. 5Dand 5F. Preferably, cathode sides 26 and insulating film sides 86 aresubstantially aligned, and gap 30 remains substantially uniformextending from exposed portions of conductive layer 14 to top surface 34of cathodes 22.

Thus it may be seen that the completed field emitter device 10fabricated in accordance with the first embodiment (FIGS. 3A-3G and4A-4D) has a structure similar to the completed device fabricated inaccordance with the second embodiment (FIGS. 3A-3G and 5A-5F). However,the size of the gap 30 provided in the first embodiment (FIG. 4A) isdetermined by the depth of the undercutting beneath the mask, whereasthe size of the gap 30 provided in the second embodiment (FIG. 5B) isdetermined by the thickness of vertical sidewalls 100 of insulative film80. Therefore, the second embodiment may provide a smaller gap than thefirst embodiment, although the second embodiment requires more stepsthan the first embodiment to produce the finished field emitter device.

It should therefore be appreciated that the above methods provideeconomical, high yielding manufacture of laterally disposed fieldemitter diodes which are well suited for use in flat panel displays.Multiple alignment steps are unnecessary. In addition, the small gapbetween the anode and cathode is provided without the need for preciselyaligning the anode above the cathode.

FIGS. 6A-6C show enlarged top plan views of a portion of field emitter10 in which anode sides 24 and cathode sides 26 assume various shapes.The shapes of sides 24 and 26 may be provided by appropriate patterningof mask 64 according to the step depicted in FIG. 3G. FIGS. 7A-7Cillustrate calculated lines of equal electrical potential across aportion of gap 30 in FIGS. 6A-6C, respectively.

In FIG. 6A, there is shown an enlarged plan view of a portion of fieldemitter device 10 wherein anode sides 24 and cathode sides 26 aresubstantially flat (stripes). In FIG. 6B, anode sides 24 are flat butcathode sides 26 are serrated (wedge-shaped). In FIG. 6C, sides 24 and26 are each serrated in a matching pattern. As is seen, gap 30 issubstantially uniform in FIGS. 6A and 6C, but is not substantiallyuniform in FIG. 6B. In FIG. 7A, equal potential lines 112 are uniformlyspaced as is expected given the flat surfaces in FIG. 6A; however, inFIG. 7B and in FIG. 7C the equal potential lines 112 converage towardpoint 114, thereby increasing the concentration of the electric fieldalong the serrated cathode sidewall 26 and increasing the fieldenhancement factor for device 10. An increased field enhancement factormay reduce or eliminate the need for a low work function cathodematerial thereby expanding the scope of cathode materials suitable forthe present invention. On the other hand, low work function materialssuch as diamond or cermets may provide suitable cathodes with flatsurfaces. While an increased field enhancement factor is generallydesirable, forming serrated sides 24 and/or 26 as compared to flat sideswill typically require smaller photolithography resolution for mask 64.For example, photolithography resolution of 25 micrometers may be smallenough for forming flat sides but too large for forming serrated sides.

Referring now to FIG. 8, there is shown an enlarged cross-sectional viewof device 10 during operation. As is seen, a stream of electrons "e" isemitted from cathode 22 across gap 30 to a major portion of surface 24of anode 16. Furthermore, in this instance anode 16 is a phosphor,substrate 12 and conductive layer 14 are transparent, and a stream ofphotons "p" generated by anode 16 flows through conductive layer 14 andsubstrate 12, respectively, thereby producing luminescence from thebottom of device 10.

Referring now to FIG. 9, there is shown an array 120 of the fieldemitter devices 10 having anodes 16 of varied phosphor materials,including ZnCd:Ag, a red phosphor 16a; ZnS:Ag,Al, a blue phosphor 16b;and ZnO:Zn, a green phosphor 16c. Conductive lines 122 connect anodes 16to bonding pads 124. Likewise conductive lines 126 connect cathodes 22to bonding pads 128. Bonding pads 126 and 128 are adapted to beconnected to other electronic components (e.g., low voltage IC drivers)in a flat panel display. Array 120 may itself define a single pixelwhich may be repeated in matrix organization to provide a full-colordisplay. Since the present method does not require precise alignment intwo planes to obtain a small gap between the anode and the cathode it isparticularly well suited for producing large area flat panel displays.

The present invention is therefore well adapted to carry out the objectsand attain the ends and advantages mentioned, as well as others inherenttherein. While presently preferred embodiments of the invention havebeen described for the purpose of disclosure, numerous other changes inthe details of construction, arrangement of parts, compositions andmaterials selection, and processing steps can be carried out withoutdeparting from the spirit of the present invention which is intended tobe limited only by the scope of the appended claims.

What is claimed is:
 1. A method of manufacturing a lateral field emitterdevice, comprising the following steps:(a) providing a substantiallyflat substrate; (b) disposing a conductive layer on the substrate; (c)disposing an anode material on the conductive layer; (d) positioning anetch mask with an opening therethrough above the anode material suchthat the anode material beneath the opening is exposed whereas the anodematerial beneath the mask is covered; (e) etching the anode materialbeneath the opening wherein the etching undercuts the anode materialbeneath the mask thereby forming an anode sidewall beneath the mask,exposing the conductive layer beneath the opening and exposing theconductive layer beneath the mask adjacent the anode sidewall; (f)depositing an insulative film the conductive layer beneath the openingwithout depositing the insulative film on the anode sidewall therebyforming an insulative film sidewall defined by the opening; (g)depositing a cathode material on the insulative film beneath the openingwithout depositing the cathode material on the anode sidewall therebyforming a cathode sidewall defined by the opening and a substantiallyuniform gap between the anode sidewall and the cathode sidewall whereinthe cathode material has a bottom surface between a top and bottomsurface of the anode material; and (h) removing the mask.
 2. The methodof claim 1, whereinstep (e) includes a wet chemical etch; step (f)includes depositing a discontinuous layer of the insulative film on thesubstrate without depositing the insulative material beneath the masksuch that a lower layer of the insulative film is disposed on theconductive layer beneath the opening, an upper layer of the insulativefilm is disposed on the mask, and the upper and lower layers of theinsulative film are separate and spaced; step (g) includes depositing adiscontinuous layer of the cathode material on the substrate withoutdepositing the cathode material beneath the mask such that a lower layerof the cathode material is disposed on the lower layer of the insulativefilm, an upper layer of the cathode material is disposed on the upperlayer of the insulative film, and the upper and lower layers of thecathode material are separate and spaced; and step (h) includes liftingoff the mask and the upper layers of the insulative film and the cathodematerial thereon.
 3. A method of manufacturing a lateral field emitterdevice comprising the following steps:(a) providing a substantially fiatsubstrate; (b) disposing a conductive layer on the substrate; (c)disposing an anode material on the conductive layer; (d) positioning anetch mask with an opening therethrough above the anode material suchthat the anode material beneath the opening is exposed whereas the anodematerial beneath the mask is covered; (e) etching the anode materialbeneath the opening thereby forming an anode sidewall defined by theopening and exposing the conductive layer beneath the opening; (f)depositing an insulative film on the conductive layer beneath theopening and on the entire anode sidewall thereby forming an insulativefilm sidewall with a lower portion adjacent the conductive layer and anupper portion adjacent the opening; (g) depositing a cathode material onthe insulative film on the conductive layer beneath the opening and onthe lower portion of the insulative film sidewall without depositing thecathode material on the upper portion of the insulative film sidewallthereby forming a cathode sidewall adjacent the lower portion of theinsulative film sidewall wherein the cathode material has a bottomsurface between a top and bottom surface of the anode material; (h)removing the upper portion of the insulative film sidewall; (i) removingthe mask; and (j) removing the lower portion of the insulative filmsidewall thereby forming a substantially uniform gap between the anodesidewall and the cathode sidewall.
 4. The method of claim 3, whereinstep(e) includes a dry etch; step (f) includes depositing a continuous layerof the insulative film on the substrate such that the insulative filmextends through the opening and covers the mask; step (g) includesdepositing a discontinuous layer of the cathode material on thesubstrate such that a lower layer of the cathode material is disposed onthe conductive layer beneath the opening and on the lower portion of theinsulative film sidewall, an upper layer of the cathode material isdisposed on the insulative film above the mask, and the upper and lowerlayers of the cathode material are separate and spaced; step (h)includes removing the insulative film in the opening and is performedbefore step (i); and step (i) includes lifting off the mask and theinsulative film above the mask and the upper layer of the cathodematerial thereon.
 5. The method of claims 1 or 3 wherein the substrateis a single insulative substrate, the conductive layer is selectivelydeposited on the substrate, and the anode material is selectivelydeposited on the conductive layer.
 6. The method of claim 5 wherein theanode material is a low energy conductive phosphor.
 7. The method ofclaim 6 wherein the substrate and the conductive layer are transparentthereby allowing luminescence from a bottom surface of the device. 8.The method of claim 6 wherein the substrate is a metal and theconductive layer is reflective thereby allowing luminescence from a topsurface of the device.
 9. The method of claims 1 or 3 wherein thecathode material has a top surface between the top and bottom surfacesof the anode material.
 10. The method of claims 1 or 3 wherein the gapextends to the exposed conductive layer.
 11. The method of claims 1 or 3wherein the gap is substantially uniform.
 12. The method of claim 11wherein the anode sidewall and the cathode sidewall are substantiallyflat and extend orthogonally above the substrate.
 13. The method ofclaim 11 wherein the anode sidewall and the cathode sidewall areserrated and extend orthogonally above the substrate.
 14. The method ofclaims 1 or 3 wherein the anode sidewall is substantially flat andextends orthogonally above the substrate, and the cathode sidewall isserrated and extends orthogonally above the substrate.
 15. The method ofclaims 1 or 3 wherein the cathode material is selected from the groupconsisting of diamond, cermet, molybdenum, and tungsten.